How the rocket fuel equation could change the future of agriculture.

Guy Coleman

“Travelling from the surface of Earth to Earth orbit is one of the most energy intensive steps of going anywhere else. This first step, about 400 kilometres away from Earth, requires half of the total energy needed to go to the surface of Mars.”

Don Pettit, NASA Flight Engineer in The Tyranny of the Rocket Equation

If you have ever watched a rocket launch either via video or been fortunate enough to see one with your own eyes, the sheer quantity of energy required to lift a spaceship off the ground is quite unfathomable. As Don Pettit says above, just exiting the Earth’s gravitational pull requires the majority of total energy required of space flight.

In comparison to your everyday car or even a plane, a rocket with 85% of its total mass as fuel just goes to show how much every additional gram of payload costs in fuel and engineering expenses. While I am by no means even remotely close to a rocket propulsion scientist, this payload mass is defined by the Tsiolovsky rocket equation, which essentially has three key components:

  1. Delta V – the change in rocket velocity
  2. Energy available in the propellant (exhaust velocity)
  3. Propellant:rocket mass fraction
Vehicle Type Percent Propellant
Large ship3
Ute (Pickup truck)3
Fighter Jet30
Cargo Jet40
Table 1 Don Pettit lists some of the propellant contributions (by weight) to common transport vehicles. Source.

Setting any two of the three variables decides the unknown one, with the first two often dictating the third (or how much available space there is for payload). Take for example SpaceX’s Falcon 9 rocket. It has a total mass of 549,050 kg and is capable of carrying 4,020 kg to Mars. Space travel is very, very energy intensive.

The implication of all this is that every gram of payload has to be very carefully controlled, with its mass optimised for the role it plays. And not just mass either, very large but light loads (less dense) would require much bigger stowage capacities, themselves would add more mass to the overall design. This incredible requirement for mass (and volume) optimisation has led to some pretty amazing technological advancements in materials science (and of course space travel has led to many tech advances across the board). Take for example space blankets, freeze dried food, water purifiers, memory foam and composite materials for lightweight tank designs. Of course many other inventions covering robotics, satellite communications and tyres have improved our way of life here on earth.

So how does this connect with agriculture? Well people, including astronauts, need to eat. While dehydrated food is still used on the International Space Station (ISS), food has come a long way from the freeze dried food in the Apollo missions. According to NASA, the food quantity is tailored to individuals so excess food is limited. Astronauts receive three meals a day, with condiments such as salt, pepper, sauce and even peanut butter all possible. Even pizza is on the menu on the ISS! This is possibly one of my favourite ISS videos:

But what about if we were to travel to Mars for an indefinite period of time, how would we spend our 4,000 kg payload with respect to food and nutrition? This question requires us to optimise not only production, but have it matched perfectly with the nutrients we require. On Earth, on ground space for sowing crops or grazing animals tends to be the limiting factor, and most production efficiency gains are related to better use of available cleared areas. As the President of Bayer Crop Science, Liam Condon, has said, “agriculture needs to solve the paradox of increasing production and preservation at the same time – literally making more with less.” But shifting this area-optimisation to mass and volume optimisation (is this a production and nutrient density question?) required for space travel leads to questions like:

  1. Are we eating a calorie and nutrient density optimised diet currently?
  2. What does a mass-optimised diet look like?
  3. How do we optimise our new production density equation (think volume/area required) for living on other planets? I.e. how do we use a very small and expensive air locked area to produce as much as we need? Are lettuce leaves going to cut it, or should we produce potatoes like on The Martian?

Fortunately, many brilliant minds have been investigating the efficiency requirements for food production on other planets. A report on How to Feed 1 million People on Mars was released in December 2019, stating:

 Food self-sufficiency can be attained within 100 years with reasonable inputs, but massive amounts of imported food would be needed in the interim. Various strategies can reduce the amount of imported food significantly, balanced against the rate at which pressurized food facilities are constructed.

Kevin Cannon and Daniel Britt, Feeding 1 Million People on Mars. Source.

It helped answer some of the above questions, suggesting lettuce was out and other intensive protein sources such as fake eggs and insects were the most efficient methods of food production. They also suggested food production and distribution on Mars would be dependent on ‘agriculture, biotech and robotics’, exciting to contemplate agriculture as fundamental to interplanetary expansion! It’s not just physicists addressing this question, food and agricultural scientists have also been tackling the challenging problem of self-sustainable, extraterrestrial food production.

A group of Chinese scientists on the Lunar Palace 1 (an experimental design of a possible lunar habitation module based on Earth), found that growing edible crops such as wheat, soybean, carrots, cucumbers and others were capable of feeding 1267 g fresh food per day, with 78% produced in situ. The meal plans used every part of the plant, with non edible waste or meal being fed to insects for insect protein. Some interesting new snack options such as fried yellow mealworm and carrot leaves with sauce were identified as both nutrient and calorific efficient foods! Interestingly, this trend towards insect protein is also occurring on Earth. Companies such as GoTerra in Australia are taking food waste and using it as feed for black soldier flies. Insects are said to have a similar macronutrient content to plants and farm animals, but produce much higher mass per unit area.

This quest to optimise food production in a whole new context is attracting interest and research collaborations from previously distinct fields. If we decide that plants and animals are required for either wellbeing or food purposes, what seeds, larvae, root stocks, soil, fertiliser, water and other key ingredients for food production would we take? This takes optimising agricultural production to the ultimate level, and is why it seems the rocket fuel equation will shape agricultural production on Earth for years to come.

This is what is so exciting about agriculture, and why everyone should be interested in where their food originates and how it is produce. The challenge of producing food in space and on another planet is just one fascinating area that requires input from a whole raft of disciplines. If you have ideas on how we can improve agriculture and food security on Earth (and in space!) then apply for the AgriEducate Essay Competition. Entries have now opened, and close on the 31st August 2020. Head over to the competition page for extra details.

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